The present invention relates to a method for high-speed rotation of image data sent in units of words, a rotation processing system for implementing the method, and an image data rotating circuit incorporated in the system.
With the development of office automation, image data processing systems have become increasingly sophisticated. As a result, a large number of inexpensive ICs for image data processing are now available, which can process image data at a much higher speed than was previously possible. A conventional rotation processing system performing image data rotation processing using such an IC is arranged as shown in FIG. 1.
Referring to FIG. 1, page memory 51 stores image data before and after rotation. A read address generated by read address generator 52 and a write address generated by write address generator 53 are selected by selector 54, and the selected address is supplied to page memory 51. Read data (RD) from page memory 51 is temporarily latched by register 55, and is then rewritten in page memory 51. For example, assume that read address generator 52 generates a read address in a direction indicated by an arrow in FIG. 2A. At that time, if write address generator 53 generates a write address in a direction indicated by an arrow shown in FIG. 2B, image data can then be rotated counterclockwise through 90 degrees. If the write address is generated as shown in FIG. 2C, image data is rotated through 180 degrees. If the write address is generated as shown in FIG. 2D, image data is rotated through 270 degrees.
In this case, the page memory used in the conventional image data rotation processing system, can be accessed in units of words (n bits) in the horizontal direction, but can only be accessed in units of bits in the vertical direction. For this reason, the 0- or 180-degree rotation processing can be performed in units of words. However, 90- or 270-degree rotation processing words must be write accessed in units of bits. Therefore, a read out word (n-bits) can be written at once during 0- or 180-degree rotation processing, while the word must be written n times during 90- or 270-degree rotation processing, and the rotation processing requires a long time.
Thus in the conventional rotation processing system, only a memory-to-memory operation is allowed. A compression/expansion processing system or an enlargement/reduction processing system employing a pipeline processing method in units of words cannot be directly connected to the rotation processing system. Thus, a processing time of the image data rotation processing system is limited.